Wall-stabilised high-pressure mercury vapour discharge lamp containing iodide

ABSTRACT

In a high-pressure mercury vapor discharge lamp containing metal iodide additions, inhomegeneity of the color of the emitted light is inhibited by a specific relation between arc voltage, arc length and diameter of the discharge space.

United States Patent [1 1 Beijer et a1.

1 Dec. 16, 1975 1 1 WALL-STABILISED HIGH-PRESSURE MERCURY VAPOUR DISCHARGE LAMP CONTAINING IODIDE [75] Inventors: Louis Benjamin Beijer; Antonius Jozephus Gerardus Cornelis Driessen; Cornelis Adrianus Joannes Jacobs, all of Eindhoven,

Netherlands [73] Assignec: U. S. Philips Corporation, New

York, NY.

[22] Filed: Mar. 23, 1971 [21] App1.No.: 127,256

[30] Foreign Application Priority Data Apr. 13, 1970 Netherlands 7005294 [52] US. Cl. 313/214; 313/184; 313/220; 313/225; 313/229 [51] Int. C1. .HOIJ 61/073; H01] 61/20; H01] 61/30 [58] Field of Search 313/184, 214, 220, 225,

[56] 1 References Cited UNITED STATES PATENTS 2,240,353 4/1941 Schnetzler 313/214 X 2,659,833 11/1953 Anderson, Jr. 313/184 X 3,450,925 6/1969 Johnson 313/225 X FOREIGN PATENTS OR APPLICATIONS 106,842 5/1939 Australia 313/214 1,555,032 12/1968 France 313/225 Primary Examiner-Palmer C. Demeo Attorney, Agent, or Firm-Frank R. Trifari [57] ABSTRACT In a high-pressure mercury vapor discharge lamp containing metal iodide additions, inhomegeneity of the color of the emitted light is inhibited by a specific relation between arc voltage, arc length and diameter of the discharge space.

2 Claims, 1 Drawing Figure US. Patent Dec. 16, 1975 INVENTORS LOUIS e. BEIJER ANTONIUS J. 6.0 DlESSEN CORNELJS AJ- JACO AGEN T WALL-STABILISED HIGH-PRESSURE MERCURY VAPOUR DISCHARGE LAMP CONTAINING IODIDE The invention relates to wall-stabilised high-pressure mercury vapour discharge lamps which in addition to mercury and a rare gas in a cylindrical discharge space contain iodide of at least one of the elements sodium, lithium, thallium, indium, tin or dysprosium.

Discharge lamps of the kind described above have been known for several years and are commonly used. As compared with the high-pressure mercury vapour discharge lamps without iodides they have the advantage of a higher light output and render a considerably better colour rendition possible. This resides in the fact that strong radiation is emitted which originates from the added elements or iodides. The iodine contained in the discharge space is necessary inter alia to introduce into discharge those elements which at the normal operating temperature of such lamps do not have a sufficient vapour pressure to be able to perform their function. The iodides of these elements readily evaporate at the normal operating temperature and in the discharge they are split up into iodine and the element in a gaseous form, which element then emits its characteristic radiation after excitation. The iodine does not substantially emit radiation.

It has been found from experiments on many known iodide lamps having a lamp voltage of from 50 to 300 Volts that different longitudinal parts of the arc discharge emit light of a slightly different colour also after reaching the stable operating condition. This is often a great drawback for the practical use of such lamps, inter alia, because consequently the shadow of objects irradiated by the lamps shows disturbing colour fringes.

An explanation of the inhomogeneity of the light as regards the colour cannot be given with assurance. It is notable that this inhomogeneity in the same lamp in a vertical operating position is often greater than in a horizontal position. There are indications that the partial vapour pressure of the iodides and the diffusion of the vapour of the iodides play a role in this phenomenon.

The inhomogeneity becomes quite clearly manifest when the discharge space of the lamp contains an excess of sodium iodide.

In the vertical operating position of such a lamp the lower portion of the arc emits radiation originating from the sodium to a greater extent than the upper portion.

The inventors surprisingly found by experiment that the above-mentioned drawback of the inhomogeneity can be reduced to an undisturbing magnitude when satisfying certain relations between the lamp voltage (which is the voltage between the electrodes in the operating condition of the lamp), the distance between the electrodes and the internal diameter of the discharge space. The advantages of such lamps such as a high output and a satisfactory colour rendition can then be fully maintained.

According to the invention a wall-stabilised highpressure mercury vapour discharge lamp for a lamp voltage of from 50 to 300 Volts which in addition to mercury and a rare gas in a cylindrical discharge space contains iodide of at least one of the elements sodium, lithium, thallium, indium, tin and dysprosium is characterized in that the distance between the electrodes and 2 the diameter of the cross-section of the discharge space have dimensions such that the equations are satisfied, wherein V is the lamp voltage in Volts, L is the distance in centimetres between the electrodes and D is the internal diameter in centimeters of the discharge space.

The structure of a lamp according to the invention is preferably such that the two equations L s l D s4 are satisfied, for in that case high light outputs (in lm/W) can be obtained.

An Example of a discharge lamp according to the invention is shown in the drawing, wherein the line p indicates the scale used.

The lamp shown in the drawing is intended for a lamp voltage of 130 Volts and a load of 2000 Watts.

The lamp includes a discharge space 1 having a quartz glass wall. The discharge space includes the electrodes 2 and 3 to which the current is applied through the seals 4 and 5 and the current supply wires 6 and 7. The discharge space 1 is suspended by means of the pinches 8 and 9 in a bracket consisting of the wires 10 and 11 and the transverse connections 12 and 13. The assembly of the discharge space together with the bracket is present in a hard-glass outer envelope 14.

The discharge space 1 contains 320 mg mercury 2 mg indium metal 400 mg Nal 30 mg "Ill 8 mg Hgl Furthermore, the discharge space contains as an ignition gas a mixture of neon and argon at a pressure of 50 Torr (at 20C). The volume ratio of argon and neon is 0.5 99.5.

The outer envelope 14 is filled with nitrogen and neon (ratio in parts by volume 40 60) at a pressure of 350 Torr.

In the above-prescribed operating conditions the output of the lamp is approximately lumens per Watt. Irrespective of the operating position of the lamp, the light emitted by the arc discharge between the electrodes 2 and 3 has a substantially white colour (colour temperature approximately 5300K), and is homogeneous throughout the distance between the electrodes 1 and 2.

What is claimed is:

1. In a wall-stabilised high-pressure mercury vapour discharge lamp having a lamp voltage of from 50 to 300 volts which in addition to mercury and a rare gas in a cylindrical discharge space contains iodide of at least one of the elements sodium, lithium, thallium, indium, tin and dysprosium, the improvement comprising that the distance between the electrodes and the diameter of the cross-section of the discharge space have dimensions such that the equations:

are satisfied, wherein V is the lamp voltage in Volts, L is the distance in centimeters between the electrodes are satisfied. 

1. IN A WALL-STABILIZED HIGH-PRESSURE MERCURY VAPOUR DISCHARGE LAMP HAVING A LAMP VOLTAGE OF FROM 50 TO 300 VOLTS WHICH IN ADDITION TO MERCURY AND A RARE GAS IN A CYLINDRICAL DISCHARGE SPACE CONTAINS IODIDE OF AT LEAST ONE OF THE ELEMENTS SODIUM, LITHIUM, THALLIUM, INDIUM, TIN AND DYSPROSIUM, THE IMPROVEMENT COMPRISING THAT THE DISTANCE BETWEEN THE ELECTRODES AND THE DIAMETER OF THE CROSS-SECTION OF THE DISCHARGE SPACE HAVE DIMENSIONS SUCH THAT THE EQUATIONS:
 2. A wall-stabilised discharge lamp as claimed in claim 1, characterized in that the two equations: 